U.S. patent application number 13/820740 was filed with the patent office on 2014-01-23 for silicone composition for elastomer foam.
This patent application is currently assigned to BLUESTAR SILICONES FRANCE SAS. The applicant listed for this patent is Delphine Blanc, Dominique Canpont. Invention is credited to Delphine Blanc, Dominique Canpont.
Application Number | 20140024731 13/820740 |
Document ID | / |
Family ID | 43530469 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140024731 |
Kind Code |
A1 |
Blanc; Delphine ; et
al. |
January 23, 2014 |
SILICONE COMPOSITION FOR ELASTOMER FOAM
Abstract
The present relates to novel organopolysiloxane compositions
intended to generate an elastomer foam (or silicone foam) with good
mechanical properties and low density low density, i.e. less than
0.35 g/cm3 and preferably less than 0.25 g/cm3.
Inventors: |
Blanc; Delphine; (Lyon,
FR) ; Canpont; Dominique; (Ternand, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Blanc; Delphine
Canpont; Dominique |
Lyon
Ternand |
|
FR
FR |
|
|
Assignee: |
BLUESTAR SILICONES FRANCE
SAS
Saint-Fons
FR
|
Family ID: |
43530469 |
Appl. No.: |
13/820740 |
Filed: |
August 25, 2011 |
PCT Filed: |
August 25, 2011 |
PCT NO: |
PCT/FR2011/000473 |
371 Date: |
August 9, 2013 |
Current U.S.
Class: |
521/86 ;
521/91 |
Current CPC
Class: |
C08G 77/20 20130101;
C08L 2205/03 20130101; C08L 83/04 20130101; F16J 15/022 20130101;
C08J 9/02 20130101; C08K 5/05 20130101; C08J 9/0023 20130101; C08K
3/36 20130101; C08J 9/0066 20130101; C08J 2383/04 20130101; C08J
9/0061 20130101; C08L 83/04 20130101; B41F 17/001 20130101; C08J
9/0042 20130101; C08G 2101/00 20130101; C08L 2205/02 20130101; C08L
83/00 20130101; C08G 77/12 20130101 |
Class at
Publication: |
521/86 ;
521/91 |
International
Class: |
C08J 9/00 20060101
C08J009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2010 |
FR |
1003553 |
Claims
1. An organopolysiloxane composition X which is a precursor of a
silicone foam, comprising: at least one polyorganosiloxane A having
a viscosity of from 10 to 300 000 mPas and exhibiting, per
molecule, at least two C.sub.2-C.sub.6 alkenyl groups bonded to
silicon, at least one polyorganosiloxane B having a viscosity of
from 1 to 5000 mPas and exhibiting, per molecule, at least two
.ident.SiH units and optionally at least three .ident.SiH units, a
catalytically effective amount of at least one catalyst C which is
a compound derived from at least one metal belonging to the
platinum group, at least one porogenic agent D, optionally at least
one diorganopolysiloxane oil E blocked at each end of a
diorganopolysiloxane chain thereof, by a triorganosiloxy unit, the
organic radicals of which bonded to the silicon atoms are selected
from alkyl radicals having from 1 to 8 carbon atoms inclusive,
optionally comprising methyl, ethyl, propyl and
3,3,3-trifluoropropyl groups, cycloalkyl groups, optionally
comprising cyclohexyl, cycloheptyl and cyclooctyl groups, and aryl
groups, optionally comprising xylyl, tolyl and phenyl, at least one
inorganic filler F which is a fumed silica, having a specific
surface area S of less than 65 m.sup.2/g, optionally less than 50
m.sup.2/g, optionally at least one additive G, and optionally at
least one polyorganosiloxane resin H, with the proviso that, the
nature and the amount of constituents are determined such that
viscosity of said organopolysiloxane composition X is less than 55
000 mPas, optionally less than 30 000 mPas and said viscosities are
dynamic viscosities measured at 25.degree. C. using a Brookfield
viscometer according to the instructions of the AFNOR NFT 76-102
standard.
2. The organopolysiloxane composition X as claimed in claim 1,
wherein the inorganic filler F is a fumed silica, the specific
surface area S of which is included in the following range 25
m.sup.2/g.ltoreq.S.ltoreq.45 m.sup.2/g.
3. The organopolysiloxane composition X as claimed in claim 1,
wherein the inorganic filler F is a fumed silica, the surface of
which has been pretreated.
4. The organopolysiloxane composition X as claimed in claim 1,
wherein the amount of the inorganic filler F is from 0.1 to 20
parts by weight per 100 parts by weight of the organopolysiloxane
composition X.
5. The organopolysiloxane composition X as claimed in claim 1,
wherein the porogenic agent D is a compound comprising a hydroxyl
function and which is not a retarder or an inhibitor of a
hydrosilylation reaction, optionally comprising an
.alpha.-acetylenic alcohol.
6. The organopolysiloxane composition X as claimed in claim 1,
wherein the porogenic agent D is a compound selected from the group
consisting of a polyol, an alcohol which is not a retarder or an
inhibitor of the hydrosilylation reaction, optionally comprising an
.alpha.-acetylenic alcohol, an organosilane or a polyorganosilane
containing at least one silanol function, and water.
7. The organopolysiloxane composition X as claimed in claim 1,
wherein the porogenic agent D is a compound selected from the group
consisting of a diol which is not a retarder or an inhibitor of the
hydrosilylation reaction, optionally comprising an
.alpha.-acetylenic alcohol, an organic alcohol having from 1 to 12
carbon atoms and having one hydroxyl function per molecule, an
organosilane or a polyorganosilane comprising at least one silanol
function, and water.
8. A two-component precursor system P for the organopolysiloxane
composition X of claim 1 said two-component system P comprising:
two distinct parts P1 and P2 intended to be mixed so as to form
said organopolysiloxane composition X; and wherein one of the parts
P1 or P2 comprises the catalyst C and the porogenic agent D and
does not comprise the polyorganosiloxane B.
9. A silicone foam capable of being obtained by crosslinking and/or
curing of the organopolysiloxane composition X as defined in claim
1.
10. A organopolysiloxane composition X as defined in claim 1
adapted for being used for pad printing.
11. A organopolysiloxane composition X as defined in claim 1,
adapted for being used for preparation of filling foams or foam
seals in construction, transportation, electrical insulation and/or
domestic electrical appliance field.
12. The organopolysiloxane composition X as claimed in claim 5,
wherein the porogenic agent D is a compound selected from the group
consisting of a polyol, an alcohol which is not a retarder or an
inhibitor of the hydrosilylation reaction, optionally comprising an
.alpha.-acetylenic alcohol, an organosilane or a polyorganosilane
containing at least one silanol function, and water.
13. The organopolysiloxane composition X as claimed in claim 5,
wherein the porogenic agent D is a compound selected from the group
consisting of a diol which is not a retarder or an inhibitor of the
hydrosilylation reaction, optionally comprising an
.alpha.-acetylenic alcohol, an organic alcohol having from 1 to 12
carbon atoms and having one hydroxyl function per molecule, an
organosilane or a polyorganosilane containing at least one silanol
function, and water.
14. A silicone foam capable of being obtained by mixing said parts
P1 and P2 of the two-component system P as defined in claim 8,
followed by crosslinking and/or curing of the resulting
composition.
Description
[0001] The present invention relates to novel organopoly-siloxane
compositions of low viscosity, i.e. less than 55 000 mPas and
preferably less than 30 000 mPas, intended to generate a foam of
silicone elastomer (also known as "silicone foam") with good
physical and mechanical properties and of low density, i.e. less
than 0.35 g/cm.sup.3 and preferably less than 0.25 g/cm.sup.3.
[0002] The expression "silicone foam" denotes a polyorganosiloxane
composition in the foam form. Silicone foams are well known in the
art and their preparation is described in a certain number of
patents.
[0003] The expression "crystalline silica" denotes a silica in its
natural form, of which quartz is one of the most widely known and
used forms, in contrast to cristobalite and tridymite, which are
much less widely used forms.
[0004] The expression "fumed silica" denotes silicas prepared by
hydrolysis at high temperature (pyrohydrolysis), in a flame, of
silicon tetrachloride SiCl.sub.4 according to the following
reaction:
##STR00001##
[0005] This chemical reaction releases a considerable amount of
heat which is evacuated in a cooling zone. The only by-product is
hydrochloric acid, which is separated at the outlet of the process
and recycled so as to form, by reaction with silicon, silicon
tetrachloride.
[0006] With regard to silicone foams, several techniques exist for
producing them. A first technique employs a condensation reaction
with release of volatile by-products. This is the case in
particular for systems using the condensation reaction of the
SiH--SiOH type, which makes it possible to release hydrogen which
then acts as a porogenic agent. For example, French patent No.
FR-A-2 589 872 describes a silicone foam precursor composition
comprising an organosilicon polymer comprising siloxane units
having hydroxyl groups bonded to the silicon, an organosilicon
polymer comprising siloxane units having hydrogen atoms bonded to
the silicon, a catalyst, for example a tin compound, and a finely
divided filler comprising silica which has been treated to become
hydrophobic. These compositions cure via a polycondensation
reaction and, although they are satisfactory in many respects, the
tin-catalyzed compositions described in French patent No. FR-A-2
589 872 are regarded as rather unsatisfactory owing to the use of a
tin catalyst, which may exert certain undesirable toxic
effects.
[0007] A variant described in U.S. Pat. No. 3,923,705 consisted in
providing compositions comprising polydiorganosiloxanes bearing
hydrogen atoms bonded to the silicon available for a condensation
reaction with polydiorganosiloxanes bearing hydroxyl groups bonded
to the silicon (silanols) in the presence of a platinum catalyst.
This reaction thus makes it possible to construct the network while
producing hydrogen gas necessary for the formation of a silicone
foam. In this type of formulation, the formation of gas is
proportional to the rate of crosslinking and consequently the
density of the foams obtained is difficult to control, thus
explaining the difficulties in obtaining low-density foams by this
technique. These compositions can also comprise a
polydiorganosiloxane bearing vinyl groups bonded to the silicon
which crosslink simultaneously via polyaddition reactions with the
polydiorganosiloxanes bearing hydrogen atoms bonded to the silicon,
thus participating in the construction of the network of the
silicone foam.
[0008] According to another variant described in U.S. Pat. No.
4,189,545, silicone foams are prepared from a composition
comprising water, a polydiorgano-siloxane bearing vinyl groups
bonded to the silicon, a polydiorganosiloxane containing hydrogen
atoms bonded to the silicon and borne by units in the chain and not
exclusively at the chain end, in order to be able to act as a
crosslinking agent. The water reacts with the polysiloxane
comprising hydride functions, thus producing hydrogen gas and a
silanol. The silanol then reacts with the polydiorganosiloxane
comprising hydride functions via a condensation reaction, thus
generating a second molecule of hydrogen gas, while another
polydiorganosiloxane bearing vinyl groups bonded to the silicon
will simultaneously react, via an addition reaction, with another
polydiorganosiloxane comprising a hydride function, thus
participating in the construction of the network of the silicone
foam. The main contribution made by this technique is that the
hydrogen gas is produced without the addition of silanol and with
the addition of a small amount of water.
[0009] In U.S. Pat. No. 4,590,222, silicone foams are prepared from
a composition comprising a polydiorganosiloxane, a resin, a
platinum-based catalyst, an organohydro-siloxane, a
polyorganosiloxane bearing hydroxyl groups on the chain-end units,
a filler and an organic alcohol.
[0010] However, techniques which use silanol as a source of
porogenic agent have a tendency to give foams having densities
which are too high for many applications, for example those
intended for the transport industry. Furthermore, when
medium-density foams are obtained, this most commonly occurs to the
detriment of the mechanical properties (tensile strength, tear
strength, etc.).
[0011] Another technique consists in using porogenic agents or
additives, added to the silicone matrix, which, under the action of
heat, expand the material: [0012] either by decomposition with
release of gas, the case in particular of derivatives of azo type,
for example azodicarbonamide, which will make it possible to
release nitrogen, carbon dioxide gas and ammonia. This type of
porogenic agent, despite the fact that it is widely used for other
materials, presents serious problems of toxicity (release of
hydrazine), [0013] or by a phase change (liquid to gas)--the case
in particular of low-boiling-point solvents.
[0014] Finally, an alternative technique consists in mechanically
introducing a gas (for example, nitrogen) into the silicone matrix
under pressure, followed by passage into a dynamic mixer, which
makes it possible to obtain foams having good characteristics;
however, they require bulky and expensive equipment.
[0015] Thus, despite the existence of the numerous techniques
mentioned above, the production of low-density (less than 0.35
g/cm.sup.3 or 0.25 g/cm.sup.3) silicone foams from a composition of
relatively low viscosity or of low viscosity (viscosity less than
55 000 mPas or than 30 000 mPas) still remains a problem which
arouses the interest of silicone producers. For example, U.S. Pat.
No. 4,418,157 describes silicone foam precursor compositions
exhibiting, before crosslinking, a viscosity of less than 100 000
mPas. As is indicated in that patent, it is known (see column 2,
lines 13 to 24) that the greater the viscosity of the composition,
the less dense the resulting foam. Thus, an advantageous approach
is described in that patent which consists in preparing a
composition having a viscosity of less than 100 000 mPas and
comprising a silicone base capable of crosslinking by polyaddition
or polycondensation, to which are added a silicone resin of "MQ"
type (nomenclature of the silicones as described, for example, in
the work by Walter Noll "Chemistry and Technology of Silicones",
Academic Press, 1968, 2.sup.nd edition, on pages 1 to 9),
optionally comprising vinyl functions, and water, which is
described as a key constituent for the creation of hydrogen gas as
described above. The addition of this specific resin makes it
possible to lower the density of the foam obtained, even though the
precursor composition is of low viscosity. However, this type of
resin is an expensive raw material, the industrial synthesis of
which requires bulky and expensive equipment.
[0016] Another example of a silicone foam precursor composition is
described in the reference WO-A-00/46282. The composition described
comprises a silicone base which crosslinks via a polyaddition
reaction (polyorganosiloxane oil comprising an .ident.SiH
function/polyorganosiloxane oils comprising an .ident.SiVi
function/Pt catalyst, with Vi=vinyl group), a compound comprising a
hydroxyl function and wollastonite (the examples describe
compositions with high levels of fillers, approximately 21 parts by
weight of fillers relative to the total weight of the composition).
It should be noted that the viscosities of the compositions
prepared in the examples (example 1, table 2) are all greater than
190 000 mPas. As is indicated above, it is known (see U.S. Pat. No.
4,418,157, column 2, lines 13 to 24) that the greater the viscosity
of the composition, the less dense the resulting foam. It will be
noted that, from the most viscous composition (reference
WO-A-00/46282, table 2, page 13, composition [1-1], viscosity of
274 000 mPam) to the least viscous composition [1-3] (viscosity=198
000 mPas), the density of the foam obtained increases (from 0.20
g/cm.sup.3 to 0.25 g/cm.sup.3), thus confirming the known teaching
relating to the difficulty in obtaining low-density foams from
compositions of low viscosity (viscosity less than 55 000 mPas or
than 30 000 mPas) before crosslinking. In point of fact, for
reasons of optimization with regard to the use of these
compositions, either by the end user or by manufacturers using
silicone foam production lines, it is vital to be able to have a
composition which, before crosslinking, is in a form of relatively
low viscosity which readily flows in the appropriate tools.
[0017] Another problem encountered in the prior art foams relates
to the sizes and the size distributions of the bubbles in the
silicone foam material. Indeed, when said bubbles are too large,
they lead to anisotropy of the physical properties according to the
points of measurement. The expression "anisotropy of the physical
properties" is intended to mean a variation in the values measured
according to the point of measurement of the silicone foam.
[0018] The expression "bubbles of small size" for a silicone foam
is intended to mean bubbles of which the width (or diameter) is
less than or equal to approximately 1 mm, the expression "bubbles
of medium size" is intended to mean that the width (or diameter) is
between 1 and 1.5 mm, whereas, for "bubbles of large size", the
width (or diameter) is greater than 1.5 mm.
[0019] For example, document WO 2007/141250 describes an
organopolysiloxane composition which is a precursor of a silicone
foam, comprising: [0020] at least one polyorganosiloxane (A)
exhibiting, per molecule, at least two C.sub.2-C.sub.6 alkenyl
groups bonded to the silicon and having a viscosity of between 10
and 300 000 mPas, [0021] at least one polyorganosiloxane (B)
exhibiting, per molecule, at least two hydrogen atoms bonded to the
silicon and preferably at least three .ident.SiH units and having a
viscosity of between 1 and 5000 mPas, [0022] a catalytically
effective amount of at least one catalyst (C) composed of at least
one metal belonging to the platinum group, [0023] at least one
porogenic agent (D) chosen from the group consisting of alkanols
comprising from 1 to 18 carbon atoms, [0024] optionally at least
one inorganic and/or metal filler (F) which may be a fumed silica
which is described as being generally characterized by a specific
surface area of between 20 and 300 m.sup.2/g, [0025] optionally at
least one additive (G), and [0026] with the additional condition
that the choice, the nature and the amount of the constituents are
determined such that the viscosity of said composition has to be
less than 50 000 mPas, preferably less than 35 000 mPas and even
more preferentially less than 15 000 mPas.
[0027] However, the compositions exemplified all contain
diatomaceous earths which do not make it possible to simultaneously
obtain good storage stability and a homogeneous foam (problem of
anisotropy of the physical properties according to the points of
measurement).
[0028] For some applications, such as pad printing (or roller
printing), specific properties of silicone foams are sought.
Indeed, pad printing is an indirect printing process. The pattern
to be printed is pre-engraved onto a backing, the plate is then
attached to a pad-printing machine, and then the ink is deposited
on the engraved parts in order to transfer the pattern onto the
object to be printed by means of a pad or a roller made of silicone
foam. In order to obtain an engraving and print of quality, it is
essential that the pad or the roller made of silicone foam consists
of bubbles of small sizes (the width or diameter is less than or
equal to approximately 1 mm) and that the size distribution of the
bubbles within the material be homogeneous so that the ink can be
deposited and transferred uniformly onto the recipient layer backed
by the layer of silicone foam while at the same time allowing a
precise reproduction of the engraving. Thus, the need to obtain
foams having bubbles of small size and a homogeneous bubble size
distribution is particularly sought for this application.
[0029] Furthermore, the silicone foam industry is always seeking
new compositions, which are silicone foam precursors, having a low
viscosity, i.e. less than 55 000 mPas or than 30 000 mPas at
25.degree. C., and capable of exhibiting good physical properties
after crosslinking.
[0030] All the viscosities with which the present account is
concerned correspond to a dynamic viscosity quantity which is
measured, in a manner known per se, at 25.degree. C. The
viscosities are measured using a Brookfield viscometer according to
the instructions of the AFNOR NFT 76-102 standard. These
viscosities correspond to a "Newtonian" dynamic viscosity quantity
at 25.degree. C., i.e. the dynamic viscosity which is measured, in
a manner known per se, at a shear rate gradient which is
sufficiently low for the viscosity measure to be independent of the
rate gradient.
[0031] However, when the formulation of low-viscosity compositions
which have siliceous reinforcing fillers in order to improve the
mechanical properties is attempted, one of the major problems
encountered is the appearance of settling, which is observed
especially after storage for a few months. Indeed, this phenomenon
is observed when these compositions are stored, for example, in the
form of a two-component system (or more commonly known as "RTV-2"
system) for compositions which can foam at room temperature. Indeed
for reasons of reactivity (crosslinking and foaming) and safety,
the components are placed in two distinct parts in order to
separate the catalysts and the porogenic agent comprising a
hydroxyl function from the silicone oil comprising an SiH group.
These settling phenomena make the composition unusable for certain
applications.
[0032] The problem considered here can therefore be summarized as
the search for a technical compromise between specifications, a
priori contradictory, for the preparation of a composition having a
low viscosity, i.e. less than 55 000 mPas or than 30 000 mPas, no
longer exhibiting a settling problem when a siliceous reinforcing
filler is used and which is a precursor of a silicone foam which
has a low density, i.e. less than 0.35 g/cm.sup.3 and preferably
less than 0.25 g/cm.sup.3, with good mechanical properties, bubble
sizes of the order of less than or equal to 1 mm and a homogeneous
bubble size distribution within the foamed material.
[0033] An objective of the present invention is thus to provide a
novel organopolysiloxane composition of low viscosity, i.e. less
than 55 000 mPas or than 30 000 mPas, which is intended to
generate, after crosslinking and/or curing, a silicone foam of low
density, i.e. less than 0.35 g/cm.sup.3 and preferably less than
0.25 g/cm.sup.3, while at the same time obtaining silicone foams
exhibiting good mechanical properties, bubble sizes of which the
width or the diameter is less than or equal to approximately 1 mm
and a homogeneous bubble size distribution within the material.
[0034] The applicant has now found, very surprisingly, that it is
possible to obtain a silicone foam of low density having a density
of less than 0.35 g/cm.sup.3 and in certain cases less than 0.25
g/cm.sup.3, bubble sizes of which the width or the diameter is less
than or equal to approximately 1 mm and a homogeneous bubble size
distribution and which is prepared from a specific composition of
which the viscosity before crosslinking is less than 55 000 mPas or
less than 30 000 mPas and which no longer exhibits a settling
problem when siliceous reinforcing fillers are used.
[0035] A subject of the invention is therefore an
organopolysiloxane composition X which is a precursor of a silicone
foam, comprising: [0036] at least one polyorganosiloxane A having a
viscosity of between 10 and 300 000 mPas and exhibiting, per
molecule, at least two C.sub.2-C.sub.6 alkenyl groups bonded to the
silicon, [0037] at least one polyorganosiloxane B having a
viscosity of between 1 and 5000 mPas and exhibiting, per molecule,
at least two .ident.SiH units and preferably at least three
.ident.SiH units, [0038] a catalytically effective amount of at
least one catalyst C which is a compound derived from at least one
metal belonging to the platinum group, [0039] at least one
porogenic agent D, [0040] optionally at least one
diorganopolysiloxane oil E blocked at each end of its chain by a
triorganosiloxy unit, the organic radicals of which bonded to the
silicon atoms are chosen from alkyl radicals having from 1 to 8
carbon atoms inclusive, such as methyl, ethyl, propyl and
3,3,3-trifluoropropyl groups, cycloalkyl groups, such as
cyclohexyl, cycloheptyl and cyclooctyl groups, and aryl groups,
such as xylyl, tolyl and phenyl, [0041] at least one inorganic
filler F which is a fumed silica, the specific surface area S of
which is strictly less than 65 m.sup.2/g, preferably strictly less
than 50 m.sup.2/g and even more preferentially less than or equal
to 45 m.sup.2/g, [0042] optionally at least one additive G, and
[0043] optionally at least one polyorganosiloxane resin H, [0044]
with the additional condition that the choice, the nature and the
amount of the constituents are determined such that the viscosity
of said organopolysiloxane composition X is less than 55 000 mPas,
preferably less than 30 000 mPas and even more preferentially less
than 25 000 mPas and said viscosities are dynamic viscosities
measured at 25.degree. C. using a Brookfield viscometer according
to the instructions of the AFNOR NFT 76-102 standard.
[0045] The applicant has discovered, fortuitously and unexpectedly,
that the use of a fumed silica, the specific surface area S of
which is strictly less than 65 m.sup.2/g and preferably strictly
less than 50 m.sup.2/g, in a composition which is a precursor of a
silicone foam, makes it possible to achieve the above-mentioned
objectives.
[0046] It is particularly advantageous to use fumed silicas, the
specific surface area S of which is included in the following range
25 m.sup.2/g.ltoreq.S.ltoreq.45 m.sup.2/g, so as to be able to find
a compromise between the desired properties.
[0047] According to one advantageous embodiment, the inorganic
filler F is a fumed silica, the surface of which has been
pretreated, for example by treatment with the various organosilicon
compounds commonly employed for this use. Thus, these organosilicon
compounds can be organochlorosilanes, diorganocyclopolysiloxanes,
hexa-organodisiloxanes, hexaorganodisilazanes,
diorganopoly-siloxanes or diorganocyclopolysilazanes (French
patents FR-A-1 126 884, FR-A-1 136 885, FR-A-1 236 505, British
patent GB-A-1 024 234).
[0048] According to one preferred embodiment, the amount of the
inorganic filler F is between 0.1 and 20 parts by weight per 100
parts by weight of the organopolysiloxane composition X.
[0049] The composition according to the invention may optionally
contain at least one reinforcing filler F', the objective of which
is to confer good mechanical and rheological characteristics on the
elastomers ensuing from the curing of the compositions in
accordance with the invention. Use may, for example, be made of
very finely divided inorganic fillers, the mean particle diameter
of which is less than 0.1 .mu.m. These fillers include fumed
silicas and precipitated silicas. These fillers can also be in the
form of more coarsely divided products, with a mean particle
diameter of greater than 0.1 .mu.m. As examples of such fillers,
mention may be made of ground quartz, diatomaceous silicas, calcium
carbonate optionally surface-treated with an organic acid or with
an ester of an organic acid, calcined clay, titanium oxide of the
rutile type, oxides of iron, zinc, chromium, zirconium, magnesium,
the various forms of alumina (hydrated or nonhydrated), boron
nitride, lithopone, barium metaborate, barium sulfate or glass
microbeads. These fillers may have been surface-modified by
treatment with the various organosilicon compounds commonly
employed for this use. Thus, these organosilicon compounds may be
organochlorosilanes, diorganocyclopolysiloxanes,
hexaorganodisiloxanes, hexaorganodisilazanes or
diorganocyclopolysilazanes (French patents FR-A-1 126 884, FR-A-1
136 885, FR-A-1 236 505, British patent GB-A-1 024 234). The
treated fillers contain, in most cases, from 3% to 30% of their
weight of organosilicon compounds. The amount used depends on the
desired mechanical properties and is generally between 0.1 and 20
parts by weight per 100 parts by weight of the organopolysiloxane
composition X.
[0050] According to one embodiment, the porogenic agent D is a
compound comprising a hydroxyl function and which is not a retarder
or an inhibitor of the hydrosilylation reaction, such as an
.alpha.-acetylenic alcohol.
[0051] Preferably, the porogenic agent D is a compound chosen from
the group consisting of a polyol, an alcohol which is not a
retarder or an inhibitor of the hydrosilylation reaction, such as
an .alpha.-acetylenic alcohol, an organosilane or a
polyorganosilane containing at least one silanol function, and
water.
[0052] Preferably, the porogenic agent D is a compound chosen from
the group consisting of a diol which is not a retarder or an
inhibitor of the hydrosilylation reaction, such as an
.alpha.-acetylenic alcohol, an organic alcohol having from 1 to 12
carbon atoms and having one hydroxyl function per molecule, an
organosilane or a polyorganosilane containing at least one silanol
function, and water.
[0053] When the porogenic agent is water, it can be introduced in
the form of an aqueous emulsion, for example an oil-in-water direct
silicone emulsion or a water-in-oil inverse silicone emulsion
comprising a silicone oily continuous phase, an aqueous phase and a
stabilizer.
[0054] Direct emulsions can be obtained by emulsification processes
well known to those skilled in the art; the process consists in
placing in an emulsion, in an aqueous phase containing a
stabilizer, for example a surfactant, a mixture of the
constituents. An oil-in-water emulsion is then obtained. The
missing constituents can then be added, either directly to the
emulsion (in the case of water-soluble constituents), or
subsequently in the form of an emulsion (in the case of
constituents soluble in the silicone phase). The particle size of
the emulsion obtained can be adjusted by means of the conventional
methods known to those skilled in the art, in particular by
continuing the stirring in the reactor for a suitable period of
time.
[0055] The inverse silicone emulsions consist of droplets of water
in a silicone oil continuous phase. They can be obtained by means
of emulsification processes well known to those skilled in the art
and which involve mixing an aqueous phase and an oily phase with or
without grinding, i.e. under strong shear. The stabilizer is
preferably chosen from the group comprising: [0056] nonionic,
anionic, cationic, or even zwitterionic surfactants; [0057]
silicone polyethers; [0058] solid particles, preferably particles
of silica optionally in combination with at least one costabilizer,
preferably selected from nonionic, anionic, cationic or even
zwitterionic surfactants; [0059] and mixtures thereof.
[0060] The surfactants are chosen more generally according to the
HLB. The term HLB (hydrophilic lipophilic balance) denotes the
ratio of the hydrophilicity of the polar groups of the surfactant
molecules to the hydrophobicity of their lipophilic component. HLB
values are in particular reported in various basic manuals, such as
the "Handbook of Pharmaceutical Excipients, The Pharmaceutical
Press, London, 1994)".
[0061] Water/silicone emulsions can also be stabilized via silicone
polyethers (Silicone Surfactants--Surfactant Science Series V86 Ed
Randal M. Hill (1999)).
[0062] Examples of porogenic agents D are, for example: [0063]
water, [0064] C.sub.1 to C.sub.12 alcohols having one hydroxyl
group, for example methanol, ethanol, n-propanol, isopropanol, a
butanol such as n-butanol, 2-butanol and tert-butanol, a pentanol,
a hexanol, n-octanol and benzyl alcohol, or [0065] polyols such as
C.sub.3 to C.sub.12 diols having two hydroxyl groups, which are
linear or branched, and which optionally comprise an aromatic ring
not functionalized with a hydroxyl group. Examples of diols are,
for example, 1,4-butanediol, 1,5-pentanediol and
1,7-heptanediol.
[0066] The polyorganosiloxane A exhibiting, per molecule, at least
two C.sub.2-C.sub.6 alkenyl groups bonded to the silicon, and
having a viscosity of between 10 and 300 000 mPas, can in
particular be formed: [0067] of at least two siloxyl units of
formula:
[0067] Y d R e SiO ( 4 - d - e ) 2 ( I ) ##EQU00001## in which:
[0068] Y is a C.sub.2-C.sub.6 alkenyl, preferably vinyl, [0069] R
is a monovalent hydrocarbon-based group with no unfavorable action
on the activity of the catalyst and is generally chosen from alkyl
groups having from 1 to 8 carbon atoms inclusive, such as methyl,
ethyl, propyl and 3,3,3-trifluoropropyl groups, cycloalkyl groups,
such as cyclohexyl, cycloheptyl and cyclooctyl groups, and aryl
groups, such as xylyl, tolyl and phenyl, [0070] d=1 or 2, e=0, 1 or
2 and the sum d+e=1, 2 or 3, and [0071] optionally of siloxyl units
having the average formula below:
[0071] R f SiO 4 - f 2 ( II ) ##EQU00002## [0072] in which R has
the same meaning as above and f=0, 1, 2 or 3.
[0073] The following compounds are examples of polyorganosiloxane
A: dimethylpolysiloxanes comprising dimethylvinylsilyl ends,
(methylvinyl)(dimethyl)polysiloxane copolymers comprising
trimethylsilyl ends or (methylvinyl)-(dimethyl)polysiloxane
copolymers comprising dimethyl-vinylsilyl ends. In the form which
is most recommended, the polyorganosiloxane A contains end
vinylsiloxy units.
[0074] Examples of polyorganosiloxane B exhibiting, per molecule,
at least two hydrogen atoms bonded to the silicon and preferably at
least three .ident.SiH units and having a viscosity of between 1
and 5000 mPas are those comprising: [0075] siloxyl units of
formula:
[0075] H g X i SiO 4 - g - i 2 ( III ) ##EQU00003## [0076] in
which: [0077] X is a monovalent hydrocarbon-based group with no
unfavorable action on the activity of the catalyst and is generally
chosen from alkyl groups having from 1 to 8 carbon atoms inclusive,
such as methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups,
cycloalkyl groups, such as cyclohexyl, cycloheptyl and cyclooctyl
groups, and aryl groups, such as xylyl, tolyl and phenyl, [0078]
g=1 or 2, preferably equal to 1, i=0, 1 or 2, and g+i=1, 2 or 3,
and [0079] optionally siloxyl units having the average formula:
[0079] X i SiO 4 - j 2 ( IV ) ##EQU00004## [0080] in which X has
the same meaning as above and j=0, 1, 2 or 3.
[0081] Appropriate polyorganosiloxanes B are
polymethylhydro-siloxanes.
[0082] The catalyst C composed of at least one metal belonging to
the platinum group is also well known. The metals of the platinum
group are those known under the name platinoids, a term which
combines together, in addition to platinum, ruthenium, rhodium,
palladium, osmium and iridium. Platinum compounds and rhodium
compounds are preferably used. Use may in particular be made of the
complexes of platinum and of an organic product described in U.S.
Pat. No. 3,159,601, U.S. Pat. No. 3,159,602 and U.S. Pat. No.
3,220,972 and European patents EP-A-0 057 459, EP-A-0 188 978 and
EP-A-0 190 530, and the complexes of platinum and of vinylated
organosiloxanes described in U.S. Pat. No. 3,419,593. The catalyst
generally preferred is platinum. Preference is given to the
Karstedt solution or complex, as described in U.S. Pat. No.
3,775,452.
[0083] The constituent E is, for example, a nonfunctionalized
linear polydimethylsiloxane, i.e. comprising repeat units of
formula (CH.sub.3).sub.2SiO.sub.2/2 and exhibiting
(CH.sub.3).sub.3SiO.sub.1/2 units at its two ends.
[0084] It is possible in particular to incorporate, as additive G,
a catalyst inhibitor in order to retard the crosslinking. Use may
in particular be made of organic amines, silazanes, organic oximes,
diesters of dicarboxylic acids, acetylenic ketones and acetylenic
alcohols (cf., for example, FR-A-1 528 464, 2 372 874 and 2 704
553). The inhibitor, when one of them is used, can be inserted in a
proportion of from 0.0001 to parts by weight, preferably 0.001 to 3
parts by weight, per 100 parts of polyorganosiloxane A. Phosphines,
phosphites and phosphonites are also among the inhibitors which can
be used in the invention. Mention may in particular be made of the
compounds of formula P(OR).sub.3 described in U.S. Pat. No.
6,300,455. All these compounds are known to those skilled in the
art and are commercially available. Mention may, for example, be
made of the following compounds: [0085] polyorganosiloxanes
substituted with at least one alkenyl which can optionally be in
cyclic form, tetramethylvinyltetrasiloxane being particularly
[0086] preferred, [0087] pyridine, [0088] organic phosphines and
phosphites, [0089] unsaturated amides, [0090] alkylated maleates,
and [0091] acetylenic alcohols which have the formula:
[0091] (R')(R'')C(OH)--C.ident.CH [0092] in which formula, [0093]
R' is a linear or branched alkyl radical or a phenyl radical;
[0094] R'' is a hydrogen atom or a linear or branched alkyl radical
or a phenyl radical; it being possible for the radicals R' and R''
and the carbon atom located in the .alpha. position with respect to
the triple bond to optionally form a ring; and [0095] the total
number of carbon atoms contained in R' and R'' being at least 5,
preferably from 9 to 20.
[0096] For said acetylenic alcohols, mention may be made, by way of
examples, of: [0097] 1-ethynyl-1-cyclohexanol; [0098]
3-methyl-1-dodecyn-3-ol; [0099] 3,7,11-trimethyl-1-dodecyn-3-ol;
[0100] 1,1-diphenyl-2-propyn-1-ol; [0101]
3-ethyl-6-ethyl-1-nonyn-3-ol; [0102] 2-methyl-3-butyn-2-ol; [0103]
3-methyl-1-pentadecyn-3-ol, and [0104] diallyl maleate or diallyl
maleate derivatives.
[0105] These inhibitors are added in an amount by weight of between
1 and 50 000 ppm relative to the weight of the total silicone
composition, in particular between 10 and 10 000 ppm and preferably
between 20 and 2000 ppm.
[0106] Mention may be made, as other additive G, of thixotropic
additives for making it possible to thicken, to a correct extent,
the silicone elastomer foam precursor compositions without for all
that affecting their fluidity necessary for handling them and in
such a way that the composition, before crosslinking, does not
spontaneously flow if this is not required. In the applications
covered by the invention, it is advisable to have a crosslinkable
composition which has rheological properties such that it can be
readily usable (good fluidity) and such that it is capable of
retaining the shape given thereto at least for the time necessary
for the crosslinking for definitively fixing the memory of the
intended shape. The silicone compositions crosslinkable in this
rheological state can be described as non-drip. It is in fact
important in these applications that the composition does not flow
in the interstices of the mold. The thixotropic additive G thus
modifies the rheological properties of the composition by giving it
a high yield point.
[0107] As thixotropic agent, mention may be made of: [0108]
ultrafine silicas in appropriate proportion; [0109] silicone
polyethers functionalized with polyethylene oxide (PEO) and/or
polypropylene oxide (PPO) functions, such as the following
commercial products: DBP-534, DBP-732, DBE-224, DBE-821, DBE-621,
DBE-814 or DBE-712 sold by the company Gelest Inc., DC-193 sold by
the company Dow Corning, or the products Tegopren.RTM.-5878,
Tegopren.RTM.-3022, Tegopren.RTM.-5863, Tegopren.RTM.-3070,
Tegopren.RTM.-5851, Tegopren.RTM.-5847 or Tegopren.RTM.-5840 sold
by the company Evonik Industries, and also the silicone polyethers
comprising siloxyl units below:
[0109] ##STR00002## [0110] (x and y being integers .gtoreq.0 with
x+y.gtoreq.1) [0111] fluorinated resins which are fluoropolymers
containing C--F bonds, such as, for example, polyvinyl fluoride,
polyvinylidene fluoride, polytetra-fluoroethylene (PTFE),
polymonochlorotrifluoroethylene, polyfluoropolyethers,
ethylene/tetrafluoroethylene copolymers,
tetrafluoroethylene/perfluorovinyl ether copolymers, or
perfluoroethylene/perfluoropropylene copolymers. Examples are
described in international patent application No. WO
2000/060011-A1, [0112] compounds based on an amine (polymer chain,
preferably silicone polymer chain, grafted with primary amine or
secondary amine functions) or on polyglycols, and [0113]
polyorganosiloxanes functionalized with cyclic amine functions and
in particular with piperidinyl functions which can be used alone or
in combination with silicas having undergone a surface treatment.
Examples are described in international patent application WO
2003/037987-A1.
[0114] The polyorganosiloxane resins H are branched
organopolysiloxane oligomers or polymers which are well known and
commercially available. They are in the form of solutions,
preferably siloxane solutions. As examples of branched
organopolysiloxane oligomers or polymers, mention may be made of
"MQ" resins, "MDQ" resins, "TD" resins and "MDT" resins, it being
possible for the alkenyl functions to be borne by the M, D and/or T
siloxyl units. Those skilled in the art in the silicone field
commonly use this nomenclature which represents the following
siloxyl units:
[0115] R.sub.3SiO.sub.1/2 (M unit), RSiO.sub.3/2 (T unit),
R.sub.2SiO.sub.2/2 (D unit) and SiO.sub.4/2 (Q unit),
[0116] with R being a C.sub.2 to C.sub.6 alkenyl group, such as a
vinyl, allyl or hexenyl group, a monovalent hydrocarbon-based group
chosen from alkyl groups having from 1 to 8 carbon atoms inclusive,
such as methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups,
cycloalkyl groups, such as cyclohexyl, cycloheptyl and cyclooctyl
groups, and aryl groups, such as xylyl, tolyl and phenyl.
[0117] The polyorganosiloxane resins H which are particularly
useful according to the invention are silicone resins comprising
"Si-alkenyl" functions, i.e. resins comprising vinyl, allyl and/or
hexenyl functions. According to one preferred embodiment of the
invention, the polyorganosiloxane resins H are vinylated silicone
resins. Advantageously, they comprise in their structures from 0.1%
to 20% by weight of alkenyl group(s). In these resins, the alkenyl
groups can be located on siloxyl units (M), (D) or (T). These
resins can be prepared, for example, according to the process
described in U.S. Pat. No. 2,676,182. A certain number of these
resins are commercially available, most commonly in the form of
solutions, for example in xylene.
[0118] For example, the polyorganosiloxane resin H comprises:
[0119] at least two different siloxyl units chosen from those of
formula:
[0119] W.sub.aZ.sub.bSiO.sub.(4-(a+b))/2 (V) [0120] in which:
[0121] the W symbols, which may be identical or different, each
represent a C.sub.2-C.sub.6 alkenyl group; [0122] the Z symbols,
which may be identical or different, each represent a
nonhydrolyzable monovalent hydrocarbon-based group which has no
unfavorable action on the activity of the catalyst, which is
optionally halogenated and which is preferably chosen from alkyl
groups and also from aryl groups, and [0123] a is 1 or 2,
preferably 1, b is 0, 1 or 2 and the sum a+b is equal to 1, 2 or 3,
[0124] and optionally units having the formula below:
[0124] Z.sub.cSiO.sub.(4-c)/2 (VI) [0125] in which Z has the same
meaning as above and c is equal to 0, 1, 2 or 3, with the condition
that at least one of the units (V) or (VI) is a T or Q unit.
[0126] In one preferred embodiment of the invention, the
polyorganosiloxane resin H is a resin which comprises Si-Vi units
(with "Vi" meaning a vinyl group) and is chosen from the group
consisting of the following silicone resins: [0127] MD.sup.ViQ
where the vinyl groups are included in the D units, [0128]
MD.sup.ViTQ where the vinyl groups are included in the D units,
[0129] MM.sup.ViQ where the vinyl groups are included in a part of
the M units, [0130] MM.sup.ViTQ where the vinyl groups are included
in a part of the M units, [0131] MM.sup.ViDD.sup.ViQ where the
vinyl groups are included in the M and D units, [0132] and mixtures
thereof, with: [0133] M=siloxyl unit of formula R.sub.3SiO.sub.1/2
[0134] M.sup.Vi=siloxyl unit of formula (R.sub.2)(vinyl)SiO.sub.1/2
[0135] D=siloxyl unit of formula R.sub.2SiO.sub.2/2 [0136]
D.sup.Vi=siloxyl unit of formula (R)(vinyl)SiO.sub.2/2 [0137]
Q=siloxyl unit of formula SiO.sub.4/2; [0138] T=siloxyl unit of
formula RSiO.sub.3/2, and [0139] the R groups, which may be
identical or different, are monovalent hydrocarbon-based groups
chosen from alkyl groups having from 1 to 8 carbon atoms inclusive,
such as methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups, and
aryl groups, such as xylyl, tolyl and phenyl.
[0140] According to another particular embodiment of the invention,
the polyorganosiloxane resin H is added to the composition
according to the invention in the form of a mixture in at least one
polyorganosiloxane oil.
[0141] According to another embodiment of the invention, the
vinylated polyorganosiloxane resin H is present in the silicone
elastomer composition before crosslinking at up to 25%, preferably
up to 20% and even more preferentially between 1% and 20% by weight
relative to the total weight of the composition according to the
invention.
[0142] The vinylated polyorganosiloxanes A, the polyorganosiloxane
resins H and the polyorganosiloxanes comprising a hydride function
B are in amounts such that a molar ratio between the .ident.SiH
functions and the .ident.SiVi functions is between 0.5 and 10 and
preferably between 1 and 6.
[0143] According to one particular embodiment of the invention, the
organopolysiloxane composition comprises: [0144] (A) 100 parts by
weight of at least one polyorganosiloxane A exhibiting, per
molecule, at least two C.sub.2-C.sub.6 alkenyl groups bonded to the
silicon, and having a viscosity of between 10 and 300 000 mPas,
[0145] (B) from 0.5 to 50 parts by weight of at least one
polyorganosiloxane B exhibiting, per molecule, at least two
hydrogen atoms bonded to the silicon and preferably at least three
.ident.SiH units and having a viscosity of between 1 and 5000 mPas,
[0146] (C) a catalytically effective amount of at least one
catalyst C composed of at least one metal belonging to the platinum
group, [0147] (D) from 0.05 to 50 parts by weight of at least one
porogenic agent D according to the invention and as described
above, [0148] (E) from 0 to 50 parts by weight of at least one
diorganopolysiloxane oil E blocked at each end of its chain by a
triorganosiloxy unit, the organic radicals of which bonded to the
silicon atoms are chosen from alkyl radicals having from 1 to 8
carbon atoms inclusive, such as methyl, ethyl, propyl and
3,3,3-trifluoropropyl groups, cycloalkyl groups, such as
cyclohexyl, cycloheptyl and cyclooctyl groups, and aryl groups,
such as xylyl, tolyl and phenyl, [0149] (F) from 0.5 to 50 parts of
at least one inorganic filler F, [0150] (G) from 0 to 10 parts by
weight of at least one additive G, and [0151] (H) from 0 to 70
parts by weight of the polyorganosiloxane resin H, [0152] with the
additional condition that the choice, the nature and the amount of
the constituents are determined such that the viscosity of said
composition is less than 55 000 mPas and preferably less than 30
000 mPas.
[0153] According to another of its aspects, the present invention
relates to a two-component precursor system P for the
organopolysiloxane composition X according to the invention and as
defined above and comprising the constituents A, B, C, D, E, F, G
and H as defined above, said two-component system S being
characterized: [0154] in that it is in two distinct parts P1 and P2
intended to be mixed so as to form said organopolysiloxane
composition X and comprising said constituents, and [0155] in that
one of the parts P1 or P2 comprises the catalyst C and the
porogenic agent D and does not comprise the polyorganosiloxane
B.
[0156] A subject of the present invention is also a silicone foam
capable of being obtained by crosslinking and/or curing of the
organopolysiloxane composition X as defined above or by mixing of
the parts P1 and P2 of the two-component system S as defined above,
followed by crosslinking and/or curing of the resulting
composition.
[0157] Another subject of the invention relates to the use of the
organopolysiloxane composition X, of the two-component system P or
of the silicone foam according to the invention and as defined
above, for pad printing or the preparation of filling foams or foam
seals in the construction, transportation, electrical insulation or
domestic electrical appliance field.
[0158] The present invention will now be described in greater
detail using embodiments taken by way of nonlimiting example.
EXAMPLES
Examples 1 to 10
Preparation of Silicone Foams which Crosslink at Room
Temperature
[0159] A two-component composition comprising the parts P1 and P2
is prepared from the constituents listed hereinafter (the exact
compositions are described in tables 1 and 2):
1) Part P1:
[0160] a: vinylated polyorganosiloxane resin comprising M, D.sup.Vi
and Q (or "MD.sup.ViQ") siloxyl units with Vi=vinyl group, M:
(CH.sub.3).sub.3SiO.sub.1/2, Q: SiO.sub.4/2, D.sup.Vi: (CH.sub.3)
(Vi) SiO.sub.2/2 [0161] b1: polydimethylsiloxane blocked by
(CH.sub.3).sub.2ViSiO.sub.1/2 units and having a viscosity of 3500
mPas at 25.degree. C. [0162] b2: polydimethylsiloxane blocked by
(CH.sub.3).sub.2ViSiO.sub.1/2 units and having a viscosity of 10
000 mPas at 25.degree. C. [0163] b3: polydimethylsiloxane blocked
by (CH.sub.3).sub.2ViSiO.sub.1/2 units and having a viscosity of 60
000 mPas at 25.degree. C. [0164] b4: polydimethylsiloxane oil
blocked at each of the chain ends by a
Vi(CH.sub.3).sub.2SiO.sub.1/2 unit, having a viscosity of 100 000
mPas at 25.degree. C. [0165] c1: fumed silica treated with a
silicone oil, having a specific surface area equal to 30 m.sup.2/g
(BET), sold under the trade name Aerosil.RTM. RY50. [0166] c3:
diatomaceous earth sold under the trade name Celite-SF. [0167] c4:
ground crystalline silica having a specific surface area equal to
3.3 m.sup.2/g, sold under the trade name Sikron B4000. [0168] c5:
ground crystalline silica surface-treated with a vinylsilane and
having a specific surface area equal to 6.5 m.sup.2/g, sold under
the trade name Silbond 8000TST. [0169] c6: fumed silica treated
with HMDZ (hexamethyldisilazane), having a specific surface area
equal to 200 m.sup.2/g (BET) and dispersed at 30% in
polydimethylsiloxane blocked by (CH.sub.3).sub.2ViSiO.sub.1/2 units
and having a viscosity of 1500 mPas at 25.degree. C. [0170] d1:
butanol or d2: silicone emulsion containing 58.45% by weight of
water. [0171] e: Karstedt platinum catalyst. [0172] f:
polydimethylsiloxane oil blocked at each of the chain ends by a
(CH.sub.3).sub.3SiO.sub.1/2 unit and having a viscosity of 1000
mPas at 25.degree. C. [0173] g: poly(vinylmethyl)(dimethyl)siloxane
oil having a D.sup.Vi unit content of 2% by weight and an M.sup.Vi
unit content of 0.4% by weight (oil with pendant vinylated
groups).
2) Part P2:
[0173] [0174] a: vinylated polyorganosiloxane resin comprising M,
D.sup.Vi and Q (or "MD.sup.ViQ") siloxyl units. [0175] b1:
polydimethylsiloxane blocked by (CH.sub.3).sub.2(Vi)SiO.sub.1/2
units and having a viscosity of 3500 mPas. [0176] b3:
polydimethylsiloxane blocked by (CH.sub.3).sub.2(Vi)SiO.sub.1/2
units and having a viscosity of 60 000 mPas at 25.degree. C. [0177]
b4: polydimethylsiloxane oil blocked at each of the chain ends by a
Vi(CH.sub.3).sub.2SiO.sub.1/2 unit, having a viscosity of 100 000
mPas at 25.degree. C. [0178] f: polydimethylsiloxane oil blocked at
each of the chain ends by a (CH.sub.3).sub.3SiO.sub.1/2 unit,
having a viscosity of 1000 mPas at 25.degree. C. [0179] i:
polydimethylsiloxane oil blocked at each of the chain ends by a
(CH.sub.3).sub.2HSiO.sub.1/2 unit. [0180] h:
polymethylhydrosiloxane oil blocked at each of the chain ends by a
(CH.sub.3).sub.3SiO.sub.1/2 unit. [0181] j: solution containing 1%
of ethynylcyclohexanol in a polydimethylsiloxane oil blocked by
(CH.sub.3).sub.2(Vi)SiO.sub.1/2 units, having a viscosity of 600
mPas at 25.degree. C.
[0182] Tables 1 and 2 hereinafter describe the compositions
tested.
TABLE-US-00001 TABLE 1 Compositions - parts by weight Counter
Counter Counter Counter Counter Example Example Example Example
Example Example Example Constituents 1 2 4 5 6 7 8 Part a 18.75
18.75 18.75 18.75 18.75 18.75 16.75 P1 b1 56.25 56.25 56.25 56.25
56.25 56.25 50.25 b4 6 6 6 6 6 6 0 c1 10 4.8 0 0 0 0 0 c2 0 0 0 0 0
0 0 c3 0 0 0 10 0 0 0 c4 0 0 0 0 10 0 0 c5 0 0 0 0 0 10 0 c6 0 0 0
0 0 0 30 d1 3 3 3 3 3 3 3 e 0.09 0.09 0.09 0.09 0.09 0.09 0.09 f 6
6 6 6 6 6 0 Part a 10 10 10 10 10 10 12 P2 b1 30 30 30 30 30 30 36
b4 30 30 30 30 30 30 22 h 18 18 18 18 18 18 18 i 7 7 7 7 7 7 7 j
0.1 0.1 0.1 0.1 0.1 0.1 0.1 f 4.9 4.9 4.9 4.9 4.9 4.9 4.9
TABLE-US-00002 TABLE 2 COMPOSITIONS: PARTS BY WEIGHT Constituents
Example 9 Example 10 Part a 18.75 21.24 P1 b1 56.25 33.31 b2 0 8 b3
0 6.86 b4 14.69 0 c1 1.5 1.5 d2 3.82 2 e 0.09 0.09 f 4.90 0 g 0 2
Part a 10 19.07 P2 b1 30 0 b3 0 28.60 b4 30 26.03 h 18 18.93 i 7
7.36 j 0 0 f 4.9 0
3) Processing:
[0183] 50 parts by volume of the component P2 are added to 50 parts
by volume of the part P1. Foaming and crosslinking are obtained
after manual mixing using a spatula, at 23.degree. C. for
approximately 30 seconds.
4) Tests
[0184] In the present account: [0185] the abbreviation "T/S" means
the tensile strength, in MPa according to the AFNOR NF T 46002
standard, [0186] the abbreviation hardness SOOH means the Shore 00
hardness, [0187] the abbreviation "E/B" means the % elongation at
break according to the previous standard, and [0188] the
abbreviation "Tr/S" means the tear strength in N/mm. [0189] the
expression "bubbles of small size" is intended to mean bubble sizes
of which the width or the diameter is less than or equal to
approximately 1 mm, while, for "bubbles of large size", the width
or the diameter is greater than 1.5 mm.
TABLE-US-00003 [0189] TABLE 3 Example Properties Example 1 Example
2 Example 9 10 Viscosity of P1 11 000 5120 9440 15 800 Settling of
P1 No No No No Density of the 0.19 0.19 0.21 0.21 crosslinked foam
(g/cm.sup.3) S00H after 7 days at 38 37 25 35 23.degree. C.
Mechanical T/S 0.21 0.19 0.10 0.20 properties after 7 E/B 63 63 72
89 days at 23.degree. C. Tr/S 0.86 0.84 0.80 1.4 Bubble size Small
Small Small Small
TABLE-US-00004 TABLE 4 Counter Counter Counter Counter Counter
Properties Example 4 Example 5 Example 6 Example 7 Example 8
Viscosity of P1 3840 5680 4520 4640 4720 Settling of P1 No Yes Yes
Yes No (<1 week) (<1 week) (<1 week) Density of the 0.23
0.18 0.18 0.18 0.24 crosslinked foam (g/cm.sup.3) S00H after 7 days
at 23.degree. C. 26 40 41 40 46 Mechanical T/S 0.18 0.17 0.15 0.15
0.10 properties after 7 E/B 73 64 53 54 47 days at 23.degree. C.
Tr/S 1.27 0.95 0.87 0.76 0.83 Bubble size Large Small Small Small
Large Bubble size dispersion hetero- hetero- geneous geneous
[0190] As shown by examples 1, 2, 9 and 10 and counter examples 4
to 8, the presence of fumed silica with a low specific surface area
according to the invention makes it possible to obtain components
(or parts) P1 which do not exhibit any problem of settling of the
filler even after several months of storage, and, after mixing with
the parts P2 and crosslinking, makes it possible to obtain foams of
low densities (less than 0.25 g/cm.sup.3) which have good
mechanical properties.
[0191] Furthermore, all the compositions according to the
invention, after mixing of the parts P1 and P2, make it possible to
obtain compositions having viscosities of less than 15 000 mPas.
[0192] Counter example 4 demonstrates the essential presence of
fillers according to the invention for obtaining low-density foams
with cells of which the sizes are homogeneous and small. [0193]
Counter examples 5, 6 and 7 demonstrate that even the presence of
crystalline silica with a low specific surface area or of a filler
of different nature than silica does not make it possible to
simultaneously obtain all the required properties, in particular
the nonsettling of the component P1. [0194] Counter example 8
demonstrates that the presence of fumed silica with a high/medium
specific surface area (BET specific surface area of 200 m.sup.2/g,
i.e. very much higher than 65 m.sup.2/g) does not make it possible
to simultaneously obtain all the required properties, in particular
the homogeneity and the size of the bubbles.
[0195] The foams obtained according to the invention are
homogeneous with pore sizes of less than or equal to 1 mm (or
"small bubbles") in contrast to the foams obtained (counter
examples 4 to 8) which exhibit either settling problems during
storage, or bubble sizes and/or a bubble size dispersion which are
too great. The best foams according to the invention are obtained
when the specific surface area of the fumed silica is between 25
and 45 g/m.
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